Survival rates of breast cancer patients could be improved if tumors are detected in their early stages or, following treatment such as chemotherapy, surgery, or radiation, residual cancer cells easily can be detected at the cellular level. The primary technique for early screening for breast cancer, i.e., x-ray mammography, is effective, but has disadvantages. The differentiation between normal tissue and cancerous tissue based on their relative density is small, causing false-positives and subjecting patients to additional testing that may be unnecessary, invasive, and often painful. Furthermore, exposure to ionizing radiation inherent to x-ray procedures limits the frequency that high-risk patients can be screened. The limited sensitivity of this technique allows small, early-stage tumors to be missed, as well as the failure to recognize residual cancer cell clusters after treatment thereby permitting the disease to progress between screenings. Implementation of new, sensitive, and safe detection methods would improve the diagnosis of breast cancer and prognosis of breast cancer patients by reducing levels of morbidity and mortality.
Fluorescence imaging using near-infrared (NIR) contrast agents is an emerging, highly sensitive method for tumor detection that takes advantage of the relative transparency of mammalian tissue to NIR light (about 700-1000 nm). A contrast agent that absorbs and emits light in the visible and NIR and accumulates specifically in tumor tissue could be optically imaged through soft tissue, thereby providing an ideal, non-invasive detection method for superficial tumors in soft tissue, such as those of the breast.
Optical absorbance/fluorescence or phosphorescence imaging of soft tissue with light at visible and near-infrared (NIR) wavelengths within the window of relative tissue transparency therefore represents an important emerging method of tumor detection, but, as with other imaging modalities, effective optical contrast agents are needed. Porphyrazines (pzs), a class of porphyrinoid macrocycles, exhibit a combination of photophysical, chemical, and biological properties that make them uniquely attractive both as optical tumor-imaging agents and as a platform for dual-mode optical/magnetic resonance (MR) imaging agents.